Constant and Cyclic-Load Creep Tests of Several Materials

This investigation was made to determine whether alternate periods of load and rest would have the same effect as continuous loading on the deformation characteristics of metals at elevated temperatures. Constant-load and cyclic-load creep tests were made on sheet specimens of 24S-T3 and 24S-T81 aluminum alloys at 300 F, SAE 4130 steel at 800 F, and AISI 310 stainless steel at 1500 F. The test results indicate that under the conditions of these tests cycling the load did not increase the rate of creep of the materials tested. Also since none of the cyclic-load tests had creep rates less than one half the rate of the constant-load test, there was no evidence of recovery taking place during the low-load part of the cycle. Specimens of 24S-T3 showed less creep deformation during the first ten hours of the tests than did the corresponding tests of 24S-T81 alloy, although subsequent creep rates were essentially the same. The data obtained, although incomplete, indicate that it is probably safe to design for cyclic-load conditions using data from constant-load tests.